Optical attenuator

Abstract

A device includes a number of grating stages having a liquid crystal layer disposed between at least two substrates, where at least one is coated with a photo-alignment layer and transparent electrodes. Each grating stage may be switchably responsive to a voltage, with grating periods of each grating stage selected such that, when the voltage is applied to a grating stage and a laser beam is passed therethrough, optical energy from the laser beam in plus and minus first orders is deflected toward sides of the grating stage and optical energy from a zero order of the laser beam is allowed to pass through the grating stage. A polarization state of the laser beam may be maintained from an input through an output. Each grating stage may include a thickness selected to achromatize the laser beam through the grating stages.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS[0001]This application claims the benefit of and priority to U.S. Provisional Application Ser. No. 62 / 509,996, entitled “Compact, High Speed, Achromatic Mid-wave Infrared Attenuator,” filed on May 23, 2017, the entirety of which is hereby incorporated by reference.[0002]This application is related to U.S. Patent Application Ser. No. 15 / 689,022, filed on even date herewith by Joshua Lentz, and entitled “Projection Using Liquid Crystal Polarization Gratings to Modulate Light” (AFD 1671), the entirety of which is incorporated by reference herein.STATEMENT OF GOVERNMENT INTEREST[0003]The invention described herein may be manufactured and used by or for the Government of the United States for all governmental purposes without the payment of any royalty.BACKGROUND[0004]Attenuation mechanisms without a polarization change relative to the source may present benefits that are frequently lost through the use of conventional attenuation schemes. However, ...

AI Technical Summary

Benefits of technology

The patent describes a device that includes multiple grating stages that can deflect and redirect laser beams passing through them. Each grating stage has a first and second substrate with photo-alignment properties and transparent electrodes. A liquid crystal layer is placed between the substrates to create a grating stage. The grating stages are switchable and can be controlled to deflect the laser beams in a way that maintains their polarization state. The device can be used to achieve optical alignment and achieve a desired polarization state for the laser beams. The technical effect of this invention is to provide a device that can efficiently and accurately align laser beams in a simple and cost-effective way.

Problems solved by technology

Attenuation mechanisms without a polarization change relative to the source may present benefits that are frequently lost through the use of conventional attenuation schemes.

However, with the advent of multi-line lasers and supercontinuum lasers, broadband attenuation has generally become relatively difficult in cases where it is desirous to maintain laser source characteristics through attenuation.

The problem may further increase in complexity if true continuous wave (CW) conditions are desirous for a system, e.g., where an attenuator does not have pulse width modulation or similar modulation mechanisms.

Unfortunately, the Inconel® coating generally does not provide even attenuation over a large spectrum of interest (e.g., about 1.9 μm-5.0 μm) and the relative spectral content of the laser may change dynamically with CVND angular position.

Thus, at least three problems may arise from the current state of the art of CVND technology: (1) multiple reflections; (2) spectrally-dependent attenuation; and (3) polarization-sensitive attenuation.

Additionally, CVNDs may require motors with significant weight, moderate size, and very large, heavy cabling to provide power and feedback signals.

However, PWM may introduce an undesirable frequency element into a CW system, which can ruin fidelity in some cases.

Similarly, source modulation through PWM is typically not an option.

For binary modulation of a DMD for attenuation, pixels may be turned on and off completely such that attenuation would be provided spatially in a laser beam, but this creates undesirable spatial artifacts in the system and increases calibration complexity.

Thin film-based attenuators may be used, but many prove inflexible for system changes such as laser source changes with different polarization states.

An additional disadvantage of this technology may include the heavy motors and associated control cabling often required to rotate the attenuators at a relatively high angular velocity and acceleration in high-speed applications.

Also, the insertion losses from two polarizers may be significant in such a mechanism, and there may be a demand for relatively high extinction ratio polarizers that can withstand high-energy laser irradiance.

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